This invention relates to the preparation of symmetrical and nonsymmetrical N,N-dialkylhydroxylamines from a nitrone. The nitrone reactant can be previously formed or, in the instant process, can be formed in situ without interfering with the eventual formation of the desired hydroxylamines.
Formation of nitrones by the reaction of an N-alkylhydroxylamine with an aldehyde or ketone is known according to the following reaction: ##STR1##
However, according to the literature, results in nitrone reduction are irregular and unpredictable. In certain instances aromatic nitrones have been reduced to the corresponding hydroxylamine. Vavon et al., C.A. 22,4502 (1928) referencing Cusmano, Gazz Chim Ital. 51, II, 306-9 (1921), report that PhN(:O):CHPh can be reduced to the hydroxylamine using H.sub.2 and Pt black. Similarly, Horner et al., Chem. Ber. 90, 2184 (1957) discloses that the nitrone PhCH.dbd.N(:O)-cyclohexyl was reduced with H.sub.2 and Pt black to give the corresponding hydroxylamine, but the reaction required three days to provide the product. Although the aromatic nitrones are known to undergo reduction, the aliphatic derivatives are believed hard to reduce and give results which are unpredictable. For example, according to Hamer et al., Chem, Rev., 64, 491 (1964) which in turn references J.A.C.S. 72, 4896 (1950) certain nitrones when treated with H.sub.2 and Raney nickel at atmospheric pressure and room temperature produced moderate yields of imine product and no hydroxylamine in the reaction product. When other reductive agents are used, such as LiAlH.sub.4, the nitrone substrate has formed the amine [see W. D. Emmons, J.A.C.S. 79, 5739 (1957)], not the hydroxylamine presently desired.
It will be noted that the prior art shows that reduction of the alkyl nitrone gives amines or, when using Raney catalysts, the imine. In both cases, under the conditions described below, one achieves the N,N-dialkylhydroxylamine. Thus the prior art evidently offers no guide as to results to be predicted from the use of any particular class of nitrone with any particular class of reducing agent.
It is highly desired to form N,N-dialkylhydroxylamines, a known class of compounds useful as oxygen scavengers in boiler feed water treatment, as described in U.S. Pat. No. 4,067,690 to Cuisia et al. It is further highly desired to have a means of forming the desired compounds using a single reaction vessel and also from the more stable (in comparison to the nitrone) N-alkylhydroxylamine.